Perhaps Electrum is computing the compressed key address? I'm not an expert on Casascius or Electrum, but you might want to find out if there is a way to get Electrum to work with the uncompressed key address, or you might want to try some other method of gaining access to the bitcoins.
Be VERY careful not to reveal that private key to anyone that is trying to help you. They could be scamming you to gain access to the private key and then could run off with your bitcoins if they can figure out how to access them.
If you are comfortable enough with the process...
I would download the bitaddress.org website to run on an offline computer and enter the private key into the "Wallet Details" page there.
That should give you BOTH the compressed key AND the uncompressed key address, so you can see if that is what your problem is.
Just wanted to say thanks to you as well. This is exactly what needed to be done.